Description of the Prior Art
The IBM 6580 Display Station (IBM is a registered trademark of International Business Machines Corporation) includes a display module which may be swivelled and/or tilted by an operator to adjust the viewing angle. The base of the display module has a central ribbed portion which is shaped to present a spherically contoured convex surface. This module is supported on a plinth which has a central spherically contoured concave surface which mates with the contoured surface on the underside of the module. The two surfaces are slidable, one over the other, to rotate and/or tilt the display module on the plinth. A shaped key-piece extends from the center of the convex surface on the underside of the module through an elongated aperture extending diagonally across the concave surface in a direction from front to back of the plinth. The shape of the key-piece serves to hold the module in place on the plinth while permitting tilting of the module within limits dictated by the key-piece movable within the confines of the elongated slot. Rotation of the module is limited by a projecting lug extending upwards from the base into the spherical convex surface of the module where it engages ribs positioned to define the permitted rotational movement of the module. Wing pieces extend down from each side of the convex surface of the module to contact the plinth to provide lateral support for the module and to limit vibration. Further details of the construction of the tilt and/or rotate feature of the display module are to be found in our co-pending European patent application No. 81101628.6 and corresponding U.S. Application Ser. No. 159,553 filed June 16, 1980, now U.S. Pat. No. 4,365,779.
IBM Technical Disclosure Bulletin Vol. 23, No. 7A, December 1980, pages 2859-60 entitled "Swivel and Tilt Mechanism for Display Unit" by S. Futatsugi and M. Koboyashi, describes a mechanism similar to that incorporated in the IBM 6850 Display Station but additionally having a locking mechanism for clamping the display module, or cabinet, on the plinth, or pedestal, in the selected tilted and rotated position. The locking mechanism consists of a T-shaped shaft, or stopper, mounted for axial movement in a central hole in the concave spherical surface of the plinth and extending through a diagonally positioned elongated slot running from front to back across the convex surface of the underside of the display module. Although axially movable, the T-shaped shaft is otherwise fixed in relation to the plinth with the cross-bar of the shaft aligned parallel to the front edge of the plinth. When assembled, the cross-bar of the shaft is only aligned with the elongated slot in the display module when the latter has been rotated through 90.degree. with respect to the plinth. The T-shaped shaft serves therefore to secure the module to the plinth in all normal viewing positions. The module may be removed from the plinth if desired by rotating through 90.degree. and lifting, allowing the cross-bar of the shaft to pass through the elongated slot. The cross-piece of the shaft is provided on its underside with a hard rubber layer which is normally held in frictional contact with the inside surface of the module base by means of a spring attached to the other end of the shaft exerting a force downwards into the plinth. This has the effect of securing the display module firmly to the plinth and locking the mechanism against inadvertent movement. When it is desired to adjust the display module swivel or tilt position, the clamp is released by means of a cam operated mechanism which lifts the shaft and thus the locking brake, constituted by the rubber coated cross-piece, from engagement with the inside surface of the base of the display module.